Tin, tin/lead, tin/antimony, and tin/bismuth electrodeposits, known collectively as solder deposits, are utilized in the finishing of electronic components. Plating formulations for the electrodeposition of these solder alloys often employ surfactants as grain refining additives. The choice of the surfactants to be included in a solder plating bath is guided by the need to produce an electrodeposit with favorable surface and mechanical properties. Further restraints on the selection of surfactants are introduced by the need for formulations which can function effectively in "high speed" plating equipment. High speed solder plating can be defined as electroplating where the pace of work requires a current density greater than 120 ASF (amps per square foot) and vigorous solution agitation. The operation of high speed plating baths requires that a minimal foam level be maintained in the operating plating solution.
Low foam surfactants have been commercially available for many years, but not all low foam surfactants are suitable for electroplating applications. The discovery of novel low foam surfactants having a useful function in solder alloy electrodeposition formulations is considered to be an advancement in the field of plating science.
U.S. Pat. No. 5,072,050 (Sanderson et al.) discloses methods for the oxidation of the secondary hydroxy group in 2-hydroxypropyl (--OCH.sub.2 CHOHCH.sub.3, oxypropylene capped) terminated nonionic surfactants. The oxidation of 2-hydroxypropyl (--OCH.sub.2 CHOHCH.sub.3) terminated polyoxyalkylene compounds yields the corresponding methyl ketone terminated materials (--OCH.sub.2 COCH.sub.3). The advantageous properties of plating formulations containing polyoxyalkylene compounds terminated with ketone (e.g., --OCH.sub.2 COCH.sub.3) have not previously been disclosed. Propoxy terminated nonionic surfactants exhibit reduced foaming after complete or partial conversion to ketone termination. Generally, a conversion (hydroxyl to ketone termination) of at least 5% has an effect in reducing foam, and significant reduction occurs in the 20% to 100% conversion range. Plating formulations containing ketone terminated polyoxyalkylene surfactants produce improved deposits when compared to compositions containing the corresponding hydroxyl terminated materials.